The present invention relates generally to rigid endoscopes used in examining body cavities. The invention particularly relates to a rigid endoscope which is impermeable to liquids and vapors used in sterilization procedures and contaminants encountered during use.
Endoscopes, such as cystoscopes, arthroscopes, broncoscopes, laparoscopes and urethroscopes, must be cleaned and sterilized after use to eliminate microorganisms and viruses on their surfaces before the instrument is used again. Numerous problems have been experienced with conventional cleaning and sterilization methods now used in the industry.
Endoscopes are typically cleaned in a glutaraldehyde solution for thirty minutes to several hours depending upon the organisms to which the scope has been exposed. In some cases, the glutaraldehyde solution has been ineffective in destroying all microbes on the endoscope, allowing subsequent patients to be exposed to the microbes. The prolonged cleaning operation also limits the amount of time in which the endoscope is available for use. Another problem associated with the cleaning solution is that it gradually deteriorates seals at the distal and proximal ends of an endoscope as it is repeatedly cleaned. After a period of usage, bodily fluids from a patient may leak through the weakened seals and contaminate the interior of the endoscope. The fluids could infect subsequent patients who are examined with the scope. Also, the cleaning solution may eventually penetrate the proximal and distal ends of the endoscope and cloud the optical lenses within the instrument. The endoscope is then inoperative because an image cannot be seen through the fogged lenses. The scope must be repaired by replacing the seals and cleaning and drying the interior of the scope so that it can be used again.
Endoscopes are often sterilized by exposing them to ethylene oxide gas for periods of up to eight hours. The lengthy sterilization process limits the time in which the endoscope is available for use. Additionally, ethylene oxide can cause serious health hazards. Ethylene oxide is an irritant and a suspected human carcinogen which may cause illness following long term exposure. It is also a safety hazard because of its high flammability. Ethylene oxide adversely affects endoscopes after repeated exposure to the gas by damaging the proximal and distal seals. Once the seals are damaged, the gas leaks into the endoscope and condenses on the optical lenses, causing them to become discolored. The ethylene oxide may also deteriorate the epoxy which holds the lenses in place. The seals and the lens system within the endoscope must be replaced before the endoscope can be used again.
Steam sterilization is recognized in the industry as the most effective sterilization technique. However, the seals of conventional endoscopes are prone to failure after frequent sterilization. The endoscopes have a variety of metals such as stainless steel, brass and chrome adjacent the seals. As an endoscope is continually heated to temperatures of up to about 325.degree. F. by the autoclave and then cooled, the metals expand and contract at different rates because the metals have differing thermal expansion coefficients. Eventually the joints between the metals and the seals are loosened and steam permeates the interior of the endoscope, clouding the lenses and necessitating repair of the scope.
Attempts have been made at limiting the internal damage to an endoscope when the seals fail. U.S. Pat. No. 4,779,613 describes an endoscope which is said to require simple repairs if water vapor enters the interior of the endoscope because of its airtight observing optical system. The observing optical system, which extends from the objective near the distal tip to the eyepiece near the proximal end, is sealed with silicone-based or epoxy-based cements or O-rings. Although the lenses within the optical system may not be fogged by water vapor within the endoscope, the water vapor may fog the exterior of the eyepiece or the interior of the eyepiece cover glass and obstruct viewing. Even though the repairs may be simplified by the airtight optical system, repairs continue to be necessary for continued use of the endoscope.
There is a need for an autoclavable rigid endoscope that withstands repeated sterilization while remaining impervious.